Why are so many words in Welsh similar to English?
I've noticed a lot of the words in the beginner lessons seem very similar to English. I was wondering if this is just a coincidence or if we've lost some words/didn't have Welsh equivalent words and had to borrow from English?
I think it is a mix of all these reasons. It is common for Welsh speakers to use English words in their Welsh if they don't know the right Welsh word or can't bring it to mind at that instant. This then leads to borrowings. The Duolingo course authors may well have shown a bias towards easier vocabulary with more borrowings.
However there is another route for common vocabulary, and that is Latin. There is a lot of Latin vocabulary in Welsh, although almost no Latin grammar. Welsh may have words that came from Latin that sound just like English words that came from Latin, or similar to English words that came from French, but ultimately from Latin.
Incidentally I read that English, whilst not borrowing lots of Welsh vocabulary, did nevertheless borrow some grammar. The "Do" tenses in English appear to come from Welsh. If you think about it, Germanic languages and French don't have constructions like "did the boys go?" "does this road lead here?" This tense apparently comes from Welsh which uses Gwneud just like that.
To ease the completely new user of Welsh into the course, but also, languages evolve - even if there a perfectly 'good' Welsh word for something, if Welsh speakers on the floor of Wales use a different word, who are "we" to not use that word? For example, "cerbyd" can mean "car", but many Welsh speakers say "car". Nearly all languages will borrow from others; English is the same, with many French, German, and Latin borrowings :)
Welsh is a very ancient language that derived from Brythonic. It is the native language for most of the island of Britain but it hasn't evolved very well. There are also welsh words in the english language though like Dad,flannel ,penguin . You need to remember that welsh is over 1,500 years old . There was no cars in those days :)
Not sure what you mean by "it hasn't evolved very well." It clearly has evolved, but "very well" would be subjective.
Welsh words in English: there are a number but not convinced by this list. Dad and Mam sound like English Dad and Mum, but it is well established that these names are similar in languages across the world, and are probably derived from the first sounds that babies make. Once babies start making intelligible sounds we naturally assume they are talking about mum, and then dad. Thus "mama", "dada".
Having said that, it may be that Dad entered English specifically from Welsh as Germanic forms favoured "fader, vater, father". Against this, the Latin form was "tata", so it is nor certain this is of Welsh origin.
Flannel is of uncertain etymology, but Welsh gwlanen - "flannel wool" - is possible, as is Old French flaine, "blanket". Perhaps the Old French is also derived from a Celtic root? Despite the apparent closer similarity to flaine, the older English form is Flannen so a link to Gwlanen is not unlikely, just not certain.
Penguin sounds just like "Pen gwyn", so "white head". Except penguins have black heads which is a fairly big (but not insurmountable) spoiler to this etymology. As Antarctic survey ships left from Cardiff, it is quite possible they (or a related bird with white heads) were named by Welsh sailors. Certainly the link was strong enough to have this as a Mastermind question in the late 1980s.
However there is another etymology that is equally likely for Penguin, and that is from the Latin pinguis, meaning fat. Support for that etymology can be found in the Dutch word for a penguin, vetgans, literally "fat goose". So the bird may have been named for its squat appearance.
Some better attested Welsh words in English would be bard, corgi, coombe (the geographical feature, also written cwm and combe) and crag.
Welsh is a modern language!
It does have ancient roots, but then all natural languages have those. It came from the earlier British/Brittonic/Brythonic with influences and loans from whoever else the locals bumped into from then onwards - Romans, Gauls, Irish, Scandanavians, Normans, Saxons, Atlantic and Mediterranean traders, various English dialects...
The rough dates for the various stages of the development of Welsh are:
Primitive Welsh c500 - c800
Old Welsh c800 - c1100
Middle Welsh c1100 - 1400
Early Modern Welsh c1400 - 1588
Late Modern Welsh 1588 - onwards (starting with Bishop William Morgan's translation of the Bible into Welsh)